This is about unwieldy large font size used for displaying posts on this forum.
For some unknown reason, the CSS sets forum posts to 20px, which is huge compared to all other normal text on this site or elsewhere. For example, the items in the "Recent comments" list are 14px, and the text in the very textbox that I am now typing in to enter a post is 12px.
The large font size for displaying posts means that one has to do an awful lot of scrolling to read a thread. And anyone posting code samples sees their code wrapped at ridiculously short line length.
To fix this, simply fix the 'p' rule in the css file: theme-options-production.css, changing the font-size attribute from 20px to 14px.